Filter media is used in a filter for filtering matter such as particulate matter from fluids and includes media for air filters, chemical filters, coolant filters, hydraulic filters, oil filters, water filters, and the like. Further, filter media is used in many consumer and industrial filtration applications such as for drinking water, swimming pools, aquaculture, waste-water recycling, oil separation, and other applications. In one example, a filter media disposed in a cartridge filter filters water input at the top of the cartridge through a fluid inlet. The filter media then filters the water with the filtered water output through a fluid outlet.
A filter medium is fabricated from a diverse range of materials such as sand, glass, asbestos, natural fibers such as wood pulp and the like, and synthetic polymers such as thermoplastics and the like. Thermoplastics are a plastic material that becomes pliable or moldable above a certain temperature and solidifies during cooling. Thermoplastics may be used to form polymeric and non-polymeric thermoplastic fibers.
A filter medium is typically designed to provide a high filtering efficiency to prevent fine particulate matter from passing through while maintaining a low pressure drop across the medium over its useful life. Further, a filter medium is typically designed for an increased useful life while not requiring frequent cleaning or replacement. However, these design requirements tend to be inversely related, requiring design trade-offs. For instance, a medium having a high filtering efficiency tends to accumulate more particulate matter resulting in a high pressure drop. The loft or thickness of a filter medium typically indicates its ability to entrap particulate matter within the medium's interstitial spaces or pores without impeding the flow of a fluid through the medium. This filtration process is commonly known as depth filtration. In contrast, surface filtration accumulates particulate matter on a surface of a medium, building a high pressure drop across the medium.
There have been many attempts to develop a filter medium having high filter efficiency while maintaining a low pressure drop across the medium. One such attempt uses nonwoven material as a two-dimensional filter. For instance, a fluid having particulate matter flows through one side of the nonwoven material of a filter and a filtered fluid flows out of the other side of the nonwoven material. Further, the filtered particulate matter forms a filter cake on the nonwoven material, resulting in reducing the effectiveness of the filter and requiring a higher pumping power to maintain operation over a longer period. In addition, the use of nonwoven material as a filter material typically suffers from fiber migration, since the fibers do not always stay in their initial positions.
In another such attempt, nonwoven material has been constructed using hollow polyester fibers to form staple fibers. These staple fibers are used to form a single sliver, which may be rolled to form the filtered media. However, the staple fibers cause undesirable fiber migration. Also, the use of hollow fibers have less tensile strength and are prone to breaking, leading to increased fiber migration.
In another such attempt, a porous, compressible filter medium is disposed between compression plates to achieve desired filtration results. The compression plates are used to vary the density and denier (linear mass density) of the fibers of the filter medium. In addition to requiring the use of compression plates, this medium also suffers from a reduced capacity to hold particulate matter in the filter bed. Further, this medium is typically limited to an upflow filter systems.
Accordingly, there is a need for improved techniques relating to a filter medium having high filter efficiency while reducing filter migration and maintaining a low pressure drop across the medium and the manufacturing thereof. In addition, other desirable features and characteristics of the present disclosure will become apparent from the subsequent detailed description and claims, taken in conjunction with the accompanying figures and the foregoing technical field and background.